New parameter to force ODCR to a single AZ

[fridim]

jira: GPTEINFRA-2334

New feature for the agnosticd_odcr module: force all AZs to be a single AZ.

Sometimes we want to provision all the instances into a single AZ (for saving costs for example).

In order to do that, one would have to redefine the reservations defined in the var agnosticd_aws_capacity_reservations to make it single-zone. Here is an example with ocp4-cluster.

From:

agnosticd_aws_capacity_reservations:
  # Bastion can have its own AZ
  az1:
  - instance_type: "{{ bastion_instance_type }}"
    instance_count: 1
    instance_platform: "{{ bastion_instance_platform }}"

  masters:
  - instance_type: "{{ master_instance_type }}"
    instance_count: 3
    instance_platform: Linux/UNIX

  # Split workers in 2 AZs if possible.  Could be the same zone.
  workers1:
  # Workers: half of workers
  - instance_type: "{{ worker_instance_type }}"
    instance_count: >-
      {{ ( worker_instance_count | int / 2 )
      | round(0, 'ceil')
      | int }}
    instance_platform: Linux/UNIX
  workers2:
  - instance_type: "{{ worker_instance_type }}"
    instance_count: >-
      {{ ( worker_instance_count | int / 2 )
      | round(0, 'ceil')
      | int }}
    instance_platform: Linux/UNIX

to:

agnosticd_aws_capacity_reservations:
  # Bastion can have its own AZ
  az1:
  - instance_type: "{{ bastion_instance_type }}"
    instance_count: 1
    instance_platform: "{{ bastion_instance_platform }}"

  - instance_type: "{{ master_instance_type }}"
    instance_count: 3
    instance_platform: Linux/UNIX

  - instance_type: "{{ worker_instance_type }}"
    instance_count: "{{ worker_instance_count }}"
    instance_platform: Linux/UNIX

To avoid the work of redefining the reservations in all the configs depending on whether the user wants a single AZ or spread across multiple AZ, we want a simple ON|OFF flag.

This PR, if applied, adds a new parameter to the agnosticd_odcr module to automatically group the reservations into one or keep the default behavior. That parameter can be controlled via the global variable agnosticd_aws_capacity_reservation_single_zone (false by default).
The advantage of doing so inside the module is that it should be transparent for the config (ocp4-cluster). No logic needed there.

If the parameter single_zone is set to true, all the reservation will target the same AZ.
All the reservations are merged into one AZ. Reservations that are the same instance_type and instance_platform are merged together and instance_count is incremented accordingly.

The result will include availability_zone value for the virtual zones, but they will all be the same.

• Add unit tests to helper functions to regroup all the reservation into
  a single AZ
• test with ocp4-cluster
  • patch install-config.yml.j2 template to actually use odcr AZs
• update Readme.adoc

SUMMARY

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

ADDITIONAL INFORMATION

Tested with:

• ansible2.9-python3.6-2021-11-30 python virtualenv
• ansible 2.9.27
• python 3.10.1